I'm sure this is just my lack of experience with linux but I just cant seem to figure it out. I'm using XUbuntu annd I have the JDK6 installed and the full screen issue is really starting to bother me so I'd like to upgrade to version 7. I've tried installing it in the software center, I've tried 'sudo su apt-get install openjdk(whatever the rest of the package name is), I've tried using a package manager, I've even uninstalled version 6 then installed it and some how I end up with version 6 still. I'm sorry, I know I'm probably missing something entirely obvious but I cant figure it out.
When you have several java versions in your machine you could use below command to change the version you required.
/usr/sbin/alternatives --config java
This will ask to choose you a number and number contains the version belongs to it.
Hope this helps you.